1. Field of the Invention
The present invention relates to a liquid filter device for eliminating impurities from liquid, and more particularly, to a liquid filter device, e.g., is connected to, e.g., an oil tank of a vacuum pump to effectively eliminate impurities from lubricating oil for the vacuum pump.
2. Description of the Prior Art
In general, the following characteristics are required for a liquid filter device for eliminating impurities from liquid:
(1) The impurities are effectively eliminated.
(2) The device is of small size.
(3) The device is economical including the cost and maintenance.
In order to satisfy these requirements, there have been provided the following types of devices:
(A) Liquid is filtrated by a filter.
(B) A plurality of electrode pairs are provided in an electrode tank. A collector such as filter paper is provided between the plurality of electrode pairs. Electrostatic coupling of liquid molecules and impurity molecules is broken to electrostatically adsorb the impurity molecules in the collector.
(C) Liquid is introduce between electrodes in an electrode tank to break electrostatic coupling of liquid molecules and impurity molecules. After the electrostatic coupling with the liquid molecules is broken, the impurity molecules are electrostatically adsorbed by adsorbent contained in an adsorption tank, and the liquid passing through the adsorbent is filtrated by a filter contained in a filter tank.
The device of the item (A) is small-sized and satisfies the aforementioned condition (1) However, whereas the same cannot filtrate impurities smaller than the mesh of the filter and cannot recycle the filtrated liquid. Thus, this device does not satisfy conditions (2) and (3).
The device of the item (B) is small-sized and satisfies the condition (1), whereas merely about 1/10 of the impurities are in direct contact with the collector to be electrostatically adsorbed by the same, while it takes time to eliminate the impurities. Further, although impurities such as dust can be eliminated, the liquid cannot be recycled. When the liquid contains moisture, the collector adsorbs the moisture to cause a short between the electrodes, and voltage cannot be applied to the liquid. Thus, this device does not satisfy the conditions (2) and (3).
The device of the item (C) can effectively adsorb the impurities as well as recycle the liquid to satisfy the condition (2). However, this device is increased in size and cost, and cannot satisfy the conditions (1) and (3).